Core Boxes and Prints. 55 is carefully varnished so as to preserve it from moisture, and present a smoother surface to the mould. Core Boxes.—The simplest kinds are such as are shewn at Figs. 8, 10, and 14, where half the core lies in each box. Pegs to unite them are formed by knocking rough rods of wood through the steel plates, Fig. 68, and then driving these into holes in the core boxes (see a, Fig. 69). The pegs need not have more than a quarter or five-sixteenths of-an-inch projection, as, if they are longer, they may stick. The exact correspondence of peg and socket is found by pressing some little object, such as a pinhead, between the boxes, and using these marks as centres. Pegs are also required to unite the halves of patterns. Wooden pegs are now greatly superseded by brass dowels (Fig. 6&a). The hollows of cylindrical core boxes are gauged by the use of a property of the semi-circle—viz., that the angle contained by it is always a right angle. So that the box may be gouged out as in Fig. 69, and tried from time to time with a set square. More complicated core boxes have been already drawn at Figs. 30, 31, 33, and 41. The last one may be noticed as a case of a box that must be loose on every side in order to effett the safe removal of the core. Core Prints.—At this point we may consider shortly the different kinds of core prints. Simple cylindrical core prints are shewn at Figs. 10, 15, 18, 37 : they require a slight taper in direction of withdrawal. Some- times it is necessary for economy to core the bolt holes in the flange of a steam pipe, especially if the holes are to be square A little consideration here of direction of withdrawal will show that, if we used prints, they would need to be of a very special kind, so they are usually dispensed with altogether, . 68 a^.